Overconfidence is a pervasive reasoning bias and refers to unwarranted confidence in ones knowledge or judgment. Most reasoning theories acknowledge that people reason both analytically and intuitively. Past research has revealed that intuitivelyoriented individuals commit more reasoning biases. The hypothesis of this study was that heuristic processing contributes to the overconfidence bias. Two hundred seventeen participants completed a general-knowledge calibration task assessing overconfidence and Epsteins Rational Experiential Inventory (REI) measuring analytic and intuitive thinking styles. Results supported the hypothesis that intuitive thinking style is a significant predictor of overconfidence.